1. Field of the Invention
The present invention relates to an image reading apparatus and a copying apparatus having the image reading apparatus.
2. Description of Related Art
Image reading apparatuses have been widely used for copying apparatuses and facsimile machines, etc. in which one reading section faces a transport path of original document, and conducts reading of multiple original documents by passing the documents through a reading position.
As represented by colorization of images, demand for high quality images is increasing for image forming apparatuses such as electrophotographic image forming apparatuses.
In order to reproduce high quality images, an image reading apparatus with enhanced performances is necessary, as well as image forming apparatus with enhanced performances.
Enhanced performances of the image reading apparatus depends largely on improvement of image capturing elements such as CCD. However, since image quality improvement by enhancing performances of the image capturing elements has a certain limitation, it is inevitable for high performance image reading to have some restrictions such as decreasing reading speed.
Patent Documents 1 and 2 propose to improve an image quality by preventing a backside ghost image (phenomenon that backside image of original document appears on a copy of front-side image), which appears when reading an original document having high optical transmittance. Namely, Patent Documents 1 and 2 propose to improve an image quality by preventing a specific phenomenon of the backside ghost image.
Patent Document 1: Unexamined Japanese Patent Application Publication No. H09-135344
Patent Document 2: Unexamined Japanese Patent Application Publication No. 2003-283824
Although, the proposals of Patent Documents 1 and 2 are to improve an image quality by preventing a specific phenomenon of the backside ghost image, as the causes to deteriorate the image quality in the course of image reading, there are many causes such as attachment of dust such as paper dust onto a reading window of the image reading apparatus, and failure in pixel units of image capturing elements such as CCD, which receives light reflected from or transmitted through an original document and converts into electrical signals. There has been no effective technical measure to prevent the image deterioration caused by these phenomena.
Further, in Patent Documents 1 and 2, since a sensor to correct the backside ghost image is the sensor exclusive for correcting the backside ghost image, in cases where an image reading apparatus is required to be used as a multifunctional apparatus such as having single face reading and double face reading function, many reading sensors are needed and the structure of the apparatus tends to become complex.